As has been discussed on Climate Science, the focus for policymakers with respect to human-caused climate change has been on predicting the increase in the global average surface temperature in the coming decades (e.g. see). This is presented, for example, as a change in the global average surface temperature due to a doubling of the atmospheric concentrations of CO2.
However, this approach has serious limitations. Not only is the ability to quantitatively measure the global average surface temperature an issue (e.g. see), but there are lags with respect to radiative forcing and the temperature response as well as the “climate sensitivity” [which should be called the “global average surface temperature sensitivity”] to the radiative forcings (e.g. see).
The adoption of heat, however, in units of Joules is a much more robust “currency” to monitor global warming and cooling (see). As has been discussed on Climate Science, most of the heat content changes within the climate system occur in the oceans. The recent Lyman et al paper on the observed ocean cooling between 2003 and 2005 (see) is a very effective example of how the change in ocean heat content can be used to diagnose radiative forcing.
Using Joules as the global warming and cooling unit of “currency”, the scientific community can present projections of its change over the coming decades, as well as the fraction that they attribute to each human- and natural-climate forcing.
For example, Jim Hansen has written (see)
“Contrary to the claim of Pielke and Christy, our simulated ocean heat storage (Hansen et
al., 2005) agrees closely with the observational analysis of Willis et al. (2004)…….
The Willis et al. measured heat storage of 0.62 W/m2 refers to the decadal mean for the
upper 750 m of the ocean. Our simulated 1993-2003 heat storage rate was 0.6 W/m2 in the upper 750 m of the ocean. The decadal mean planetary energy imbalance, 0.75 W/m2, includes heat storage in the deeper ocean and energy used to melt ice and warm the air and land. 0.85 W/m2 is the imbalance at the end of the decade.”
The value presented in this Hansen comment 0f 0.85 W/m2 indicates that for the period 2000-2009, we should see a climate system accumulation of heat of 1.36 X 10**23 Joules.
The observations reported in Lyman et al indicate
“We observe a net loss of 3.2 (± 1.1) X 10**22 J of heat from the upper ocean between 2003 and 2005.” [3.2 X 10**22 Joules = 0.32 X 10 **23 Joules]
Clearly, the radiative imbalance for the remainder of this decade must be greater than presented by Jim Hansen to compensate for this heat loss.
To assess the forecast of climate system heat content change, the frequent update of ocean heat storage change should be a major priority. Rather than focusing on a global average surface temperature to monitor global warming (or cooling), the scientific and policy communities need to move to the assessment of heat itself as the currency.